Structural Support Scheme for the Replacement of Trailing Portions of Sails

ABSTRACT

A sail for a wind-powered craft includes a web which forms a flying shape upon engagement with the wind, flying shape extending from leading to trailing edges. The web includes a combination of wind-impermeable and wind-permeable portions disposed between the leading and trailing edges, with a permeability ratio of wind-permeable area to wind-impermeable area within a range of about 5 to 80 percent.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Patent Application Ser. Nos. 61/712,458, entitled Structural Support Scheme for the Replacement of the Clew Section of Sails, filed on Oct. 11, 2012, and 61/721,054, entitled A Structural Support Scheme for the Replacement of the Clew Section of Sails, filed on Nov. 1, 2012, the contents, both of which, are incorporated herein by reference in their entireties for all purposes.

BACKGROUND

1. Technical Field

This invention relates to a sail configured to fly in its working shape while being lighter and having less drag relative to its lift characteristics, than conventional sails. In spinnaker and jib embodiments, the sail may have a better ratio of lift to heeling moment, and allow tighter sheeting angles with less backwinding of the mainsail, respectively.

2. Background Information

Sails used on sailboats (and on wind powered craft in general) propel the boat in substantially all points of sail other than perhaps dead downwind, by creating “lift”. Those skilled in the art will recognize that “lift” is a low pressure zone on one side of the sail that is created by wind blowing over the convex surface of a sail when disposed in its working (flying) shape. This flying shape thus resembles a foil or airplane wing shape, to draw the craft from the high pressure area on the concave side of the sail, to the low pressure area on the convex side, to move the craft forward. The structure of the sail itself creates drag as it moves through the air, which tends to resist the forward motion of the craft.

It is desirable to provide a sail that provides a relatively large lifting force with a relatively low drag force.

SUMMARY

According to one aspect of the invention, a sail for a wind-powered craft includes a web which forms a flying shape upon engagement with the wind, the web including a combination of wind-impermeable and wind-permeable portions disposed between the leading and trailing edges, wherein the web has a permeability ratio of wind-permeable area to wind-impermeable area within a range of about 5 to 80 percent.

According to another aspect of the invention, a sail for a wind-powered craft includes: a head portion configured for being coupled to an upper end of a mast; a tack portion configured for being coupled to a deck, bowsprit, or spinnaker pole of the craft; and a clew portion configured for being coupled to one or more control lines for trimming the sail. A web supported between the head, tack and clew portions includes a combination of one or more wind-impermeable portions in the form of fabric or similar material, and one or more wind-permeable portions in the form of widely spaced strings or lines, the wind-permeable portions extending from the clew portion on a trailing portion of the sail. A ratio of the wind-permeable portions to wind-impermeable portions is within a range of about 10-40 percent. The sail is asymmetrical, or symmetrical wherein wind-permeable portions are disposed symmetrically on opposite sides of the sail with the clew and tack portions being interchangeable depending on the orientation of the craft.

In still another aspect of the invention, a method for configuring a sail for providing wind-powered motive force to a craft, includes configuring a web for forming a flying shape upon engagement with the wind, the flying shape extending from a leading edge to a trailing edge. The method also includes providing the web with a combination of one or more substantially wind-impermeable portions and one or more substantially wind-permeable portions disposed between the leading and trailing edges. The web is provided with a permeability ratio of wind-permeable area to wind-impermeable area within a range of about 5 to 80 percent.

The features and advantages described herein are not all-inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and not to limit the scope of the inventive subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements and in which:

FIG. 1 is a perspective view of a sailboat employing three sail types of the prior art;

FIG. 2 is a view similar to that of FIG. 1, with the three sail types modified schematically in accordance with the present invention; and

FIG. 3 is a schematic diagram of an alternate embodiment of the present invention.

DETAILED DESCRIPTION

In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, specific aspects in which the invention may be practiced. These aspects are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other aspects may be utilized. It is also to be understood that structural, procedural and system changes may be made without departing from the spirit and scope of the present invention. In addition, well-known structures, circuits and techniques have not been shown in detail in order not to obscure the understanding of this description. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents.

Where used in this disclosure, the term “axial” when used in connection with an element described herein, shall refer to a direction which is substantially parallel to the longitudinal axis of a wind-powered craft, such as axis a of FIG. 1. The term “wind” refers to movement of air relative to a craft and/or sail, and “motive force” refers to a force acting on the craft in a manner that provides “lift” as described above. The term “leading edge” refers to that edge of the sail that the wind hits first and the “trailing edge” or “leech” is that edge that the wind hits last as it passes over the sail. The term “leading portion” refers to a portion of the sail extending from the leading edge, and the term “trailing portion” or “leech portion” refers to a portion of the sail extending from the trailing edge or leech.

Referring now to FIGS. 1-3, aspects of the present invention will be described in detail. As shown in FIG. 1, a conventional sailboat 10 has three conventional wind-impermeable sails, i.e., a mainsail 12, a jib 14 and a spinnaker 16. As shown, these prior art sails, like virtually all sailboat sails, each have a head 18 configured for attachment to an upper end of a mast, a tack 20 configured for attachment near the deck or bowsprit or spinnaker pole, and a clew 22 at a corner of the sail to which the control lines for trimming may be attached.

The present inventor has recognized that in many sails, under many operating conditions, an area extending from the clew 22 in substantially all directions along the sail (hereinafter the “clew area” or “clew portion”) provides a relatively small amount of the total lift provided by the sail. This clew area may vary in size, depending on sail trim and specific shape of a given sail. In particular examples, it may be as large as substantially all of the axially extending portion of the sail, e.g., in the event the sail is a spinnaker. In the case of a jib, this clew area may be the trailing portion of the sail that shows “return” (i.e., is backwinding the mainsail) when the jib is tightly trimmed. A mainsail may also exhibit such a clew area under particular trimming conditions.

Turning now to FIG. 2, aspects of the present invention include a sail that provides reduced drag area, without substantial loss of “lift” area, by removing wind-impermeable sail material from the clew area (trailing portion in general), and replacing it with a wind-permeable portion(s) configured to permit wind to pass therethrough while still supporting the sail while flying in its otherwise conventional “working” shape, and while also still allowing for trimming from the conventional clew position of the sail. In the embodiments shown and described herein, the wind-impermeable portion is fabricated from conventional sail material, including various textiles/fabrics or sheet material from which sails are conventionally fabricated. The wind-permeable portion may be a series of “lines”, “open meshes” (kite wire, strings, lines, or generally narrow strips of material) that allow air to pass substantially freely therethrough. Such a sail has the advantage of being lighter than a conventional sail due to the differential weight of the wind-impermeable “fabric” relative to the wind-permeable support configuration.

As shown in FIG. 2, in each of the three otherwise conventional sails, 12′, 14′, 16′, wind- impermeable web in the clew area has been replaced with wind-permeable portions 30 in accordance with the teachings of the present invention. It will be understood that this FIG. 2 is shown for illustrative purposes only, and that the actual area of wind-permeable portions 30 may be larger or smaller than that shown. In addition, a plurality of wind-permeable portions may be provided, which may be spaced from one another on the sail. Moreover, embodiments greater or fewer numbers or types of sails, without departing from the scope of the present invention.

In the particular examples shown, the wind-permeable portions 30 may take the form of a system of “strings” 32 that allow air to pass through, and which are disposed so that the portions 30 effectively extend from the clew 22 in substantially all directions, to form the “clew area”. The size and shape of the “clew area” of a particular sail may vary depending on the sail's purpose (runner, reacher, jib, etc.) and anticipated application, as will be discussed in greater detail hereinbelow. Moreover, as discussed above, the area of fabric removal need not extend continuously as shown, but may be discontinuous, e.g., disposed as a series of patches disposed in spaced relationship to one another along the sail. The wind permeable portion also may not necessarily include the clew 22 itself. In particular embodiments, however, the wind-permeable portion is disposed closer to the trailing edge or leech 34 of the sail, than to the leading edge 36 of the sail, as best shown with respect to sail 12′.

As mentioned, the size of the wind-permeable portion is not limited to those shown in the Figures, but rather, may depend on various factors, such as the sail type (e.g., main sail, jib, spinnaker, runner, reacher, etc., including whether the sail is asymmetrical or symmetrical), the particular application, including type of craft (e.g., sailboat) and the trim or wind direction relative to the direction of movement of the craft.

In particular aspects of the invention, the wind-permeable portion(s) is sized and shaped to provide the sail with a ratio of the wind-permeable portion(s) to wind-impermeable portion(s) (hereinafter, the “permeability ratio”) within a range of about 5 to 80 percent. In other aspects, the ratio may be within a range of about 10 to 40 percent. Moreover, in various aspects, the wind-permeable area may extend, in a direction substantially parallel to the foot 37 of the sail, a distance between about 2 to 50 percent of the length of the foot. In particular embodiments, this distance may be between about 5 to 20 percent of the length of the foot. The wind-permeable area may also extend, in a direction substantially parallel to the leech 38 of the sail, a distance between about 2 to 95 percent of the length of the leech. In particular embodiments, this distance may be between about 5 to 60 percent of the length of the leech.

It is contemplated that in particular embodiments, the ratio of wind-permeable to wind-impermeable portions will be fixed for a given sail, and that users may simply maintain an inventory of sails of different ratios. The user may then choose from among the sails of various ratios, e.g., based on current wind conditions, etc.

In other embodiments, instead of a fixed ratio, sails may be provided with a variable ratio, such that a user may adjust the ratio of a particular sail. For example, a sail may be provided with a series of removable web portions, which may be selectively removed and replaced by the user, such as may be desired to respond to changing wind/weather conditions. Alternatively, in the event the wind-permeable portions are formed by a series of lines or strings as shown, such lines may be configured for being lengthened or shortened to change the shape of the sail, and/or to change the permeability ratio. These lines, whether of fixed length (for fixed ratio) or adjustable length (for variable ratio), may terminate at the clew 22 (e.g., at a clew ring or similar attachment point) of the sail as shown, where they may be connected to a conventional control sheet.

As mentioned above, the size, shape and ratio of the wind-permeable area for a particular sail may be configured based on the desired application, and may thus depend on factors such as the intended sail shape/function, intended sheeting angle, and/or angle of attack to the wind.

It should also be recognized that in accordance with the teachings hereof, the wind-permeable area may be applied to substantially any portion of the sail to which wind is not expected to be “attached” during its anticipated operation. One skilled in the art will recognize that such areas may be identified by examining telltales along the body of a conventional sail. The area of non-attached flow along, for example, the foot and leech of the sail in the embodiments shown in FIG. 2, may then replaced by a wind permeable system as described herein. The skilled artisan will also recognize, in light of the teachings hereof, that the areas of conventional sails at which the wind is not “attached” may be determined by employing well-known computer simulations using conventional computational fluid dynamic algorithms looking for attached flow or pressure differentials under various operational (e.g., wind, sheet, angle of attack, etc.) conditions.

The sail, including both the wind-impermeable and wind-permeable portions may be fabricated from any number of suitable materials. The wind-impermeable portions may be fabricated from any number of materials conventionally used for sails, including fabrics made from natural or synthetic fabrics, plastics, composite materials, mixtures of the same, and/or laminates of the same. Examples of such materials include synthetic materials such as: polyamide (Nylon); polyethylene terephthalate such as DACRON® (DuPont); aramid such as KEVLAR® (DuPont), TWARON® (Teijin Aramid), and TECHNORA® (Teijin Aramid); carbon fiber; HMPE (high molecular weight polyethylene) such as SPECTRA® (Honeywell), and DYNEEMA® (DSM IP Assets B.V.); thermoset liquid crystalline polyoxazole, such as ZYLON® (Toyo Boseki Kabushiki Kaisha Corporation), etc.

These same materials may be used to fabricate the lines or strings of the wind-permeable portions. In this regard, the lines may be fabricated from substantially any material capable of supporting the load (e.g. spectra) of the sail. The number of strings and associated attachment points may vary depending upon the load and desired working (flying) shape of the sail.

As mentioned above, it should be recognized that aspects of the present invention may be applied to symmetric, as well as asymmetric, sails. The embodiments shown and described hereinabove with respect to FIG. 2 include asymmetrical sails (e.g., a main sail, jib, and spinnaker), in which the clew, head, and tack are disposed at fixed locations on the sail regardless of the orientation of the boat. In other words, the same portions of the sail respectively serve as the clew, head, and tack regardless of whether the boat is sailing at a port tack, a starboard tack, or dead downwind. For example, those skilled in the art will recognize that to jibe a conventional spinnaker, the clew is taken from one side and passed to the opposite side of the boat, to effectively turn the spinnaker inside out on opposite jibes.

Turning now to FIG. 3, an embodiment of the present invention includes a symmetrical sail (such as a spinnaker as shown), in which the clew and tack may be interchanged with one another, e.g., based on the orientation of the boat. In this regard, the spinnaker 16″ may be moved from one side of the boat to the opposite side of the boat (i.e., the spinnaker does not turn inside out as does the asymmetrical sail discussed hereinabove), so that the location of the sail that was the tack effectively becomes the clew, and vice versa. This may be accomplished by physically detaching the tack from the spinnaker pole, pulling the sail across the boat, and then attaching what was the clew to the spinnaker pole so that it now becomes the tack.

In this alternate embodiment, both of the “clew areas” of the sail, i.e., those areas on opposite sides of the sail that alternate between clews and tacks depending on the orientation of the craft, may be replaced with strings or other wind-permeable portions 30′ as shown.

This approach effectively permits an otherwise conventional asymmetric spinnaker to be configured as a symmetric spinnaker in which the conventional head 18 is attached to the mast as shown, while the tack is replaced by an attachment 40 to the bow sprit in the middle of the foot 37 of the sail. The foot may be attached centrally to the bow sprit or alternatively, may be configured to slide along the bow sprit, e.g., between points “A” and “B” as shown, to provide the sail with greater range of movement from side to side of the boat.

It should be recognized that aspects of the invention may include various placements and shapes of the particular areas defined by the removed sail fabric. Although the present invention has been described with reference to specific exemplary aspects, it will be evident that various modifications and changes may be made to these aspects without departing from the broader spirit and scope of the invention. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.

In addition, although the present invention has been described with reference to sails used to move a sail boat, it should be recognized that aspects of the present invention may be applied to substantially any type of craft configured to support a flexible material in a working shape configured to generate a motive (lift) force. Examples of such craft may include various types of sail boats ranging from sail boards and kite surfers to large multi-masted vessels, and various aircraft, including gliders, hang gliders, ultra-light aircraft, parachutes, powered parachutes, etc.

It should be further understood that any of the features described with respect to one of the aspects or embodiments described herein may be similarly applied to any of the other aspects described herein without departing from the scope of the present invention. 

Having thus described the invention, what is claimed is:
 1. A sail for providing wind-powered motive force for a craft, the sail comprising: a web configured for forming a flying shape upon engagement with the wind, the flying shape extending from a leading edge to a trailing edge; said web including a combination of one or more substantially wind-impermeable portions, and one or more substantially wind-permeable portions, said wind-permeable portions being disposed between the leading and trailing edges; and the web having a permeability ratio of wind-permeable area to wind-impermeable area within a range of about 5 to 80 percent.
 2. The sail of claim 1, wherein the permeability is fixed.
 3. The sail of claim 1, wherein the wind-permeable portions are configured to support the flying shape of the wind impermeable portion.
 4. The sail of claim 1, wherein the permeability ratio is within a range of about 10 to 40 percent.
 5. The sail of claim 1, wherein the flying shape is disposed in the form of at least one of an upwind mainsail, a headsail, a reaching sail, a downwind sail, spinnaker, a code zero, and a jib.
 6. The sail of claim 1, wherein the flying shape is disposed in the form of a downwind sail.
 7. The sail of claim 1, wherein the flying shape is asymmetrical.
 8. The sail of claim 1, wherein the flying shape is symmetrical.
 9. The sail of claim 8, comprising a clew portion and a tack portion, the clew portion and tack portions being interchangeable with one another depending on the orientation of the craft.
 10. The sail of claim 8, wherein said wind-permeable portions are disposed symmetrically on opposite sides of the sail.
 11. The sail of claim 1, wherein the wind-permeable portion comprises a plurality of spaced lines.
 12. The sail of claim 11, wherein the sail comprises a leading portion and a trailing portion, the wind-permeable portion being disposed within the trailing portion.
 13. The sail of claim 12, wherein the wind-permeable portion extends within a clew portion of the sail.
 14. The sail of claim 11, wherein the plurality of spaced lines are selected from the group consisting of strings, ropes, ribbons, meshes, and combinations thereof.
 15. The sail of claim 11, fabricated from materials selected from the group consisting of natural fabrics, synthetic fabrics, plastics, composite materials, synthetic materials, polyamide, polyethylene terephthalate, aramid, carbon fiber; HMPE (high molecular weight polyethylene), thermoset liquid crystalline polyoxazole, and mixtures and laminates thereof.
 16. The sail of claim 1, having a foot extending along one edge of the sail, and a leech extending along another edge of the sail, the foot and leech each terminating at a clew, wherein the wind-permeable portion extends in a direction substantially parallel to the foot, for a distance between about 2 to 50 percent of the length of the foot.
 17. The sail of claim 16, wherein the wind-permeable portion extends in a direction substantially parallel to the foot, for a distance between about 5 to 20 percent of the length of the foot.
 18. The sail of claim 16, wherein the wind-permeable portion extends in a direction substantially parallel to the leech, for a distance between about 2 to 95 percent of the length of the leech.
 19. The sail of claim 18, wherein the wind-permeable portion extends in a direction substantially parallel to the leech, for a distance between about 5 to 60 percent of the length of the leech.
 20. The sail of claim 1, further comprising: a head portion configured for being coupled to an upper end of a mast disposed on the craft; a tack portion configured for being coupled near a deck, bowsprit, or spinnaker pole of the craft; and a clew portion configured for being coupled to one or more control lines for trimming the a web supported between said head portion, said tack portion, and said clew portion.
 21. A sail for providing wind-powered motive force for a craft, the sail comprising: a head portion configured for being coupled to an upper end of a mast disposed on the craft; a tack portion configured for being coupled to a deck, bowsprit, or spinnaker pole of the craft; a clew portion configured for being coupled to one or more control lines for trimming the sail; a web supported between said head portion, said tack portion, and said clew portion; said web including a combination of one or more substantially wind-impermeable portions in the form of fabric or similar material, and one or more substantially wind-permeable portions in the form of widely spaced strings or lines, the wind-permeable portions extending from the clew portion on a trailing portion of the sail; a ratio of the wind-permeable portions to wind-impermeable portions within a range of about 10-40 percent; and the sail being asymmetrical, or symmetrical wherein wind-permeable portions are disposed symmetrically on opposite sides of the sail with the clew and tack portions being interchangeable depending on the orientation of the craft.
 22. A method for configuring a sail for providing wind-powered motive force to a craft, the method comprising: configuring a web for forming a flying shape upon engagement with the wind, the flying shape extending from a leading edge to a trailing edge; providing the web with a combination of one or more substantially wind-impermeable portions and one or more substantially wind-permeable portions disposed between the leading and trailing edges; and providing the web with a permeability ratio of wind-permeable area to wind-impermeable area within a range of about 5 to 80 percent. 